Rock Lake, Lower Crawfish River Watershed (UR02)
Rock Lake, Lower Crawfish River Watershed (UR02)
Rock Lake (830700)
1364.58 Acres
Natural Community
Natural communities (stream and lake natural communities) represent model results that use predicted flow and temperature based on landscape features and related assumptions. Ranges of flow and temperature associated with specific aquatic life communities (fish, macroinvertebrates) help biologists identify appropriate resource management goals. Wisconsin Natural Communities.
Deep Lowland
Year Last Monitored
This is the most recent date of monitoring data stored in SWIMS. Additional surveys for fish and habitat may be available subsequent to this date.
Trout Water 
Trout Waters are represented by Class I, Class II or Class III waters. These classes have specific ecological characteristics and management actions associated with them. For more information regarding Trout Classifications, see the Fisheries Trout Class Webpages.
Outstanding or Exceptional 
Wisconsin has designated many of the state's highest quality waters as Outstanding Resource Waters (ORWs) or Exceptional Resource Waters (ERWs). Waters designated as ORW or ERW are surface waters which provide outstanding recreational opportunities, support valuable fisheries and wildlife habitat, have good water quality, and are not significantly impacted by human activities. ORW and ERW status identifies waters that the State of Wisconsin has determined warrant additional protection from the effects of pollution. These designations are intended to meet federal Clean Water Act obligations requiring Wisconsin to adopt an 'antidegradation' policy that is designed to prevent any lowering of water quality - especially in those waters having significant ecological or cultural value.
Impaired Water 
A water is polluted or 'impaired' if it does not support full use by humans, wildlife, fish and other aquatic life and it is shown that one or more of the pollutant criteria are not met.

Fish and Aquatic Life

Current Use
The use the water currently supports. This is not a designation or classification; it is based on the current condition of the water. Information in this column is not designed for, and should not be used for, regulatory purposes.
Deep Lowland
Deep lowland lake describes the depth and location of the lake in a watershed. These variables affect the lakes response to watershed variables.
Attainable Use
The use that the investigator believes the water could achieve through managing "controllable" sources. Beaver dams, hydroelectric dams, low gradient streams, and naturally occurring low flows are generally not considered controllable. The attainable use may be the same as the current use or it may be higher.
Supported Aquatic Life
Waters that support fish and aquatic life communities (healthy biological communities).
Designated Use
This is the water classification legally recognized by NR102 and NR104, Wis. Adm. Code. The classification determines water quality criteria and effluent limits. Waters obtain designated uses through classification procedures.
Default FAL
Fish and Aquatic Life - Default Waters do not have a specific use designation subcategory but are considered fishable, swimmable waters.


Rock Lake is a borderline high-quality mesotrophic lake. It has been the focus of long-term trend monitoring from 1986 to 1998. In 1999 and 2000, DNR baseline monitoring was conducted on Rock Lake. Ongoing monitoring indicates good water quality, but lake fertility is increasing (WDNR, 1994). This increased fertility may lead to more algae blooms. The lake was chemically treated in the past to control excessive aquatic plant growth, but this management practice has decreased due to potential harm to fish habitat. The lake has a diverse sport fishery supporting both smallmouth and largemouth bass, walleye, northern pike and panfish. A fish consumption advisory exists for walleye; past fish tissue monitoring has found elevated levels of mercury in walleye. The source of the metal is unknown (WDNR, 1994); it may originate from natural sources.

Polluted runoff is the greatest threat to Rock Lake. Residential development along the shoreline and backlot development adjacent to the lake have recently accelerated. Agricultural runoff carrying excess nutrients to the lake also contributes to water quality concerns.

A lake planning grant was awarded to the Rock Lake Improvement Association to develop an overall lake management plan. Other lake planning grants may be needed to address other issues. Rock Lake is monitored through WDNR's self-help monitoring programs. The least darter, a fish on the state's watch list, has been observed in Rock Lake (Fago,1982).

In 1999, the Rock Lake was designated by the DNR Nonpoint Source Pollution Project as a Priority Lakes Nonpoint Source Pollution Control Project. A plan was written and the implementation process in underway. The project will end in 2004.

In 2002, the county acquired 89 acres of wetlands, uplands, and woodlands on the western shore of Rock Lake. The land was purchased for development of a county park.
Also in 2002, Jefferson County obtained a DNR Lakes Planning Grant to conduct a lake classification project in the county. A Citizens Advisory Group was formed of diverse stakeholders in the county to develop a plan to increase protection of the lakes in the county.

Date  2002

Author   Aquatic Biologist

Historical Description

Source: 1968, Surface Water Resources of Jefferson County Rock Lake, T7N, R13E, Section 10, 11, 14, 15

A large compound depression in the ground moraine, which has a shoreline greatly altered by the construction in 1865 of a dam with about a 10 foot head. The southern basin of the lake is largely the result of impoundment and is sometimes referred to as Marsh Lake. The fishery consists of northern pike, walleye, yellow perch, largemouth and smallmouth bass and most panfishes. Carp are present but not in problem proportions. The lake is quite fertile and generally clear. There is a 3.1 acre city park and a 15.5 acre county park on its banks. The county park has an improved boat launching site with adequate parking. About 1,700 acres of wetland lie within this watershed and encompass Mud Lake and Bean Lake to the south. The west shore is somewhat marshy and has been the object of some dredging and shore alteration in the past. Large numbers of coots are common; mallards, teal and geese also frequent the lake especially the south lobe (Marsh Lake). The city of Lake Mills borders more than one-third of the shoreline.

Surface Acres = 1,371.0, S.D.F. = 1.43, Maximum Depth = 56 feet

Date  1968

Author   Surface Water Inventory Of Wisconsin

Rock Lake, Lower Crawfish River Watershed (UR02) Fish and Aquatic LifeRock Lake, Lower Crawfish River Watershed (UR02) RecreationRock Lake, Lower Crawfish River Watershed (UR02) Fish Consumption

General Condition

Sandy Beach East, Ferry Park Beach, and Bartel's Beach, all but one of Rock Lake's beaches, were assessed in the 2022 cycle for E. coli and found to be in good condition. These beaches are not considered impaired.

Date  2022

Author  Ashley Beranek

Impaired Waters

Rock Lake - Sandy Beach West was evaluated for bacteria in the 2022 cycle; E. coli levels were above listing thresholds as outlined in 2022 WisCALM. This beach was added to the 2022 Impaired Waters List.

Date  2022

Author  Ashley Beranek

Impaired Waters

Rock Lake (830700) was placed on the impaired waters list for Mercury in fish tissue in 1998. This water was assessed during the 2016 listing cycle; total phosphorus and chlorophyll sample data were clearly below 2016 WisCALM listing thresholds for the Recreation use and Fish and Aquatic Life use. This lake is considered impaired for Fish Consumption use and meeting REC and FAL uses.

Date  2015

Author  Aaron Larson


Wisconsin has over 84,000 miles of streams, 15,000 lakes and milllions of acres of wetlands. Assessing the condition of this vast amount of water is challenging. The state's water monitoring program uses a media-based, cross-program approach to analyze water condition. An updated monitoring strategy (2015-2020) is now available. Compliance with Clean Water Act fishable, swimmable standards are located in the Executive Summary of Water Condition in 2018. See also the 'monitoring and projects' tab.



Shoreland Monitoring, Assessment, Inventory
Shoreland Monitoring, Assessment or Inventory
Monitoring Ecosystem
Monitor or Assess Watershed Condition
Diagnostic/Feasibility Assessment
Lakes Planning Grant
Informational Meetings
Monitor Water Quality or Sediment
Lake Management Plan Development
Shoreland Monitoring, Assessment, Inventory
Korth Park Shoreline Restoration: cost share additional (to LPT-234-04) shoreline grading of 700 feet of shore to establish a stable shoreline for the long-term.
Shoreland Monitoring, Assessment, Inventory
Jefferson County Parks Department will implement the Korth Park Shoreline Restoration project along 1,300 feet of shoreline on Rock Lake. Project deliverables include: re-establishing native shoreland, upland and aquatic vegetation, stabilizing the shoreline and grading to reduce steep slopes and existing erosion.
Shoreland Ordinance
Jefferson County Parks Department will implement the Korth Park Shoreline Restoration project along 1,300 feet of shoreline on Rock Lake. Project deliverables include: re-establishing native shoreland, upland and aquatic vegetation, stabilizing the shoreline and grading to reduce steep slopes and existing erosion.
Land Acquisition
Jefferson County purchase 91.5 acres on Rock Lake for county park and open space purposes. Jefferson County will acquire property for lake protection purposes. The preservation of these parcels are for open space and passive recreation use.
Lake Classification
Jefferson County Land and Water Conservation Department will undertake a lake classification process. The resulting lake classification system will enable the County and other lake management entities to implement appropriate lake management strategies in a priority -driven and efficient manner. It will result in the protection and restoration of the water quality and natural ecosystems of the lakes in Jefferson County.
Monitor Fish Tissue
Nine Key Element Plan
Rock Lake PWS Plan - Nine Key Element Plan - The Rock Lake Priority Watershed Project plan assesses the nonpoint sources of pollution in the Rock Lake Watershed and guides the implementation of nonpoint source control measures. These control measures are needed to meet specific water resource objectives for Rock Lake and its tributaries. The purpose of this project is to reduce nonpoint source pollution to Rock Lake, and to enhance and protect the water quality of Mud, Marsh, and Bean Lakes which are also located in the Rock Lake Watershed.

Management Goals

Wisconsin's Water Quality Standards provide qualitative and quantitative goals for waters that are protective of Fishable, Swimmable conditions [Learn more]. Waters that do not meet water quality standards are considered impaired and restoration actions are planned and carried out until the water is once again fishable and swimmable

Management goals can include creation or implementation of a Total Maximum Daily Load analysis, a Nine Key Element Plan, or other restoration work, education and outreach and more. If specific recommendations exist for this water, they will be displayed below online.


Monitoring the condition of a river, stream, or lake includes gathering physical, chemical, biological, and habitat data. Comprehensive studies often gather all these parameters in great detail, while lighter assessment events will involve sampling physical, chemical and biological data such as macroinvertebrates. Aquatic macroinvertebrates and fish communities integrate watershed or catchment condition, providing great insight into overall ecosystem health. Chemical and habitat parameters tell researchers more about human induced problems including contaminated runoff, point source dischargers, or habitat issues that foster or limit the potential of aquatic communities to thrive in a given area. Wisconsin's Water Monitoring Strategy was recenty updated.

Grants and Management Projects

Monitoring Projects

Watershed Characteristics

Rock Lake is located in the Lower Crawfish River watershed which is 177.65 miĀ². Land use in the watershed is primarily agricultural (66.50%), grassland (11.20%) and a mix of wetland (10.70%) and other uses (11.60%). This watershed has 331.66 stream miles, 1,780.53 lake acres and 12,199.86 wetland acres.

Nonpoint Source Characteristics

This watershed is ranked Low for runoff impacts on streams, Not Available for runoff impacts on lakes and High for runoff impacts on groundwater and therefore has an overall rank of High. This value can be used in ranking the watershed or individual waterbodies for grant funding under state and county programs.However, all waters are affected by diffuse pollutant sources regardless of initial water quality. Applications for specific runoff projects under state or county grant programs may be pursued. For more information, go to surface water program grants.

Natural Community

Rock Lake is considered a Deep Lowland under the state's Natural Community Determinations.

Natural communities (stream and lake natural communities) represent model results and DNR staff valiation processes that confirm or update predicted conditions based on flow and temperature modeling from historic and current landscape features and related variables. Predicated flow and temperatures for waters are associated predicated fish assemblages (communities). Biologists evaluate the model results against current survey data to determine if the modeled results are corect and whether biological indicators show water quaity degradation. This analysis is a core component of the state's resource management framework. Wisconsin's Riverine Natural Communities.

Deep lowland lake describes the depth and location of the lake in a watershed. These variables affect the lakes response to watershed variables.